Entomology

Animal Sciences
COPYRIGHT 2002 The Gale Group Inc.

Entomology

Entomology is the study of insects. It is a major branch of animal zoology. Insects are one of the most successful and diverse groups of living organisms in the world today. Approximately 1.5 million species of insects have been identified by scientists as of the end of the twentieth century. However, it is estimated there may be as many as twice that number on Earth. The number of insect species is greater than the number of all other species of organisms combined. It is estimated that there are about 200 million insects for every living human. Insects are members of the kingdom Animalia, the phylum Arthropoda, and the class Insecta. Insects share the major group Arthropoda with creatures such as crabs, lobsters, shrimp, spiders, scorpions, ticks, mites, centipedes, and millipedes. Common insects include ants, butterflies, bees, cockroaches, beetles, flies, grasshoppers, mosquitoes, dragonflies, moths, wasps, and termites.

Insects have a tough exoskeleton (external skeleton) and three pairs of walking legs. The majority of insects have wings, and those with wings have two pairs, except flies, which have only one pair. Their bodies are divided into three regions: the head, thorax, and abdomen. All insects hatch from an egg in a form which is different from that of the adult insect. A well-known example of this is the caterpillar (the larval stage) and butterfly (the adult stage). Insects are characterized by their small sizes and short lifespans.

Scientists believe that insects have inhabited Earth for about 380 million years. They occupy nearly every type of environment except for salt water. They are most numerous in tropical climates and on land. Their enormous success is believed to be due to three main factors: their exoskeleton, size, and diet. Their tough exoskeleton protects them against physical damage and water loss. Their small size allows them to occupy many small areas unavailable to larger animals. Small size also allows for a faster reproductive rate. Finally, insects eat almost anything and everything.

Insects play many important roles in nature. Insects such as bees, butterflies, moths, and flies pollinate flowering plants. Many insects aid in the decomposition process and nutrient cycling, or exchange. Insects are important food sources for other animals, such as birds, and also eat other insects, thus keeping insect populations in control.

Most entomologists work in the field of economic entomology, which is also called applied entomology. They study the small minority of insects that are harmful to humans. Harmful insects include those that destroy crops and buildings and those that transmit diseases to humans. Insects that feed on plants such as grasshoppers destroy plant crops and timber. Other insects transmit plant diseases. Insects such as termites destroy wood buildings. Bloodsucking insects such as mosquitoes, lice, and fleas transmit some of the most serious infectious diseases in the world. These include malaria, dengue fever, yellow fever, bubonic plague, and typhus.

Scientists attempt to reduce the number of insect pests through a variety of ways. Cultural controls include the draining of swamps where mosquitoes breed. Chemical controls include the use of pesticides and insect repellants. Biological controls include the use of animals that naturally prey on insect pests.

People are also inadvertently decreasing the number of insects by destroying their natural habitats. Destruction of natural areas by human activities
is wiping out species of insects that we will never even know existed. What wondrous creatures are we missing?

Entomology

World of Forensic Science
COPYRIGHT 2005 Thomson Gale

Entomology

Entomology is the study of insects and their life cycles. Many insects live and feed on dead flesh, which is why entomology is relevant to forensic science . The forensic entomologist can help estimate time of death by looking at which insects are present on a corpse and where they are in their life cycle. Entomology can also shed light on the nature of injuries, whether a corpse has been moved, and whether drugs were involved in a death.

A newly deceased corpse attracts flies. Within minutes of a death, blowflies will start to lay their eggs in moist areas such as the nose, mouth, armpit, groin, or open wounds. The eggs hatch into larvae or maggots within 24 hours and these grow to around half an inch in length after about three days. Then, over the next six to ten days, they will develop into pupae with a hard outer case. Adult flies emerge about twelve days after this. If the corpse is not recovered by this time, the life cycle repeats itself so that flies at all different stages of development may be recovered from the corpse.

The forensic entomologist can use the life cycle of the flies found on a corpse as a kind of clock, giving the minimum time that elapsed since the time of death and the time of discovery. If eggs are found, it suggests death occurred less than 24 hours before discovery. The presence of maggots indicates the death occurred less than ten days ago. Pupae and mature flies will suggest a time of death one to three weeks before discovery of the corpse. However, the life cycle of flies is not an accurate clock. Flies are cold-blooded and their activities are dictated by the weather. Maggots may become dormant if it is cold and flies do not lay eggs at night. If someone is killed at midnight, flies will not appear till daylight, which means time must be added to the estimated time of death.

Because flies feed on human tissue, their own tissue can sometimes be used to measure levels of any drugs that may have played a role in the person's death. This is useful when the corpse itself does not yield tissue for analysis. Insect ecology varies from place to place and sometimes the species found on a corpse are not native to the place where the corpse is found. This may indicate that the corpse
was moved after death. Furthermore, flies feed on open bleeding wounds and their presence may help distinguish between ante-mortem and post-mortem injuries.

see also Time of death.

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entomology

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

entomology, study of insects, an arthropod class that comprises about 900,000 known species, representing about three fourths of all the classified animal species. Insects are studied because of their importance as pollinators for fruit crops; as carriers of bacterial, viral, and fungal diseases; as parasites of humans or livestock; as destroyers of economically important plants; or as predators of other destructive insects. The role of insects in ecosystems and their control by insecticides or by biological methods are studied in ecology. Some insects such as the fruit fly, Drosophila, are used in the laboratory to study genetics; others are used to study behavior and physiology. The ability to increase productivity of insect populations that supply commercially important products such as dyes, silk, and honey and the deliberate introduction of insect diseases into populations of insect pests involves knowledge of microbiology and biochemistry as well as entomology.

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